This invention relates to dispersing agents. In a particular aspect this invention relates to polymerizable alkanolamine derivatives having utility as dispersing agents.
Powder coatings were developed as an alternative to solvent based coatings as a means of eliminating the volatile solvents from the environment. The development has been described by Emory P. Miller and David D. Taft in "Fundamentals of Powder Coatings," published by the Society of Mechanical Engineers, 20501 Ford Road, Dearborn, Michigan, 1974. The coating is formulated as a dry powder consisting of one or more thermoplastic or thermosetting resin film-formers, or binders, and the pigments necessary to give the desired color. Sometimes a plasticizer for the film-former is included. These materials are finely cominuted and are applied to a metallic substrate by such methods as the fluidized bed process, electrostatic powder spraying, electrostatic fluidized bed and other electrostatic application methods.
Such coatings have been very successful but several problems have been encountered; also the equipment required to operate the various processes is very expensive. One of the most vexing problems is that of segregation of powders of different densities. It has been found that the ingredients must all have nearly equivalent densities to prevent segregation and subsequent non-homogeneous coating.
Another problem encountered is that of difficulty in controlling the film thickness. For example, when the powder is applied by electrostatic attraction, any inadequacies involved in applying the electrostatic charge will lead to uneven coating thickness. Also there is an inherently maximum film thickness which may prove inadequate for the anticipated use. Other problems involve those of occupational hygiene due to dust in air and the risk of explosion of the dusts. Accordingly an improved and a less expensive process is needed to utilize these coatings to the best advantage.
It is known from U.S. Pat. Nos. 3,737,401 and 3,787,230 to apply these powder coatings, not only in dry form but also wet with a liquid which is not a solvent for the particles. These patents are incorporated herein by reference thereto. According to these patents, the powders are slurried in the liquid without use of a suspending of dispersant agent. Such slurries have many disadvantages, such as lack of stability. On the other hand, the use of any of the common dispersing agents weakens the film and renders it water sensitive because the dispersing agent remains in the film after baking but does not of itself contribute to the strength, durability and water resistance possessed by the film-formers. Also some of these dispersants migrate to the surface, giving it a greasy feel, and they also attract dirt, thus marring the appearance.
E. P. Hoffman and R. P. Sikorski in the U.S. Pat. No. 3,787,230 proposed as a solution to these problems to form a slurry of the powder paint in water using a surfactant known as AEROSOL-T, a polypropylene base, non-water soluble powder. Although successful coatings are applied by this method, it suffers from the disadvantage that the slurries are not stable, i.e. the powder paint particles rapidly separate from the aqueous slurry, so best results are obtained only while continuously agitating the slurry during the coating process.